1. Field of the Invention
The present invention relates to a light-emitting lamp using a light-emitting device and an illumination device using the same, and more particularly to an illumination device for a liquid crystal display device.
2. Description of the Prior Arts
A light-emitting diode (LED) that is a semiconductor light-emitting device has been used as a light source for various illumination devices or display devices. It is roughly classified into a lamp-type LED frequently used for a popular electronic equipment and having a cannonball-shaped emitting surface and a chip-type LED frequently used for an illumination device of a liquid crystal display device.
This chip-type LED has high luminous efficiency, reduced power consumption and high durability, so that it has been used as a light source for a backlight that is an illumination device of a transmissive-type liquid crystal display device or a light source for a frontlight that is an illumination device of a reflective-type liquid crystal display device.
In the aforesaid backlight, light emitted from an LED light source arranged on an edge surface (irradiated surface) of a light-guiding plate is transmitted through the light-guiding plate, and then, emitted from an emitting surface, that is the upper surface of the light-guiding plate, due to the action of the shape of the light-guiding plate. There is a need to emit light from the light-guiding plate by using the LED light source, that is a point light source, as a surface light source. Therefore, frequently used techniques for scattering light to eliminate non-uniform brightness on the emitting surface of the light-guiding plate include forming a diffusion pattern on the front or back surfaces of the light-guiding plate or disposing a diffusion sheet at the side of the emitting surface (upper surface) of the light-guiding plate.
Further, the light emitted from the light-guiding plate having the diffusion sheet formed thereon or from the diffusion sheet via the light-guiding plate is emitted in such a manner of spreading in frontward all directions. Therefore, the product under the trade name BEF manufactured by 3M Co., Ltd., for example, is disposed as a condensing prism film. This condensing prism film enhances an efficiency of a backlight by combining two principles of refraction and reflection. The light emitted from the backlight is condensed at a view angle up to 70 degrees, while the light outside of the view angle is reflected again to be recycled in the backlight system, thereby being condensed in a direction of a display user at an optimum angle.
Moreover, the product under the trade name D-BEF manufactured by 3M Co., Ltd. is disposed as a reflective-type deflection film, whereby the emitted light is selectively reflected without being absorbed by a polarizing plate below a liquid crystal panel. Consequently, the emitted light is reused over a whole view angle of the liquid crystal panel, thereby enhancing brightness in the front direction.
However, arranging the condensing prism film, reflective-type deflection film or diffusion sheet at the side of the emitting surface of the light-guiding plate increases a thickness of the backlight unit, thereby entailing a problem of increasing cost. Further, a backlight that has recently been proposed, like a technique disclosed in the patent document 1 or in the non-patent document 1, in which polarization of emitted light is aligned, has a problem of not sufficiently achieving the original object for aligning the polarization of light emitted from the light-guiding plate, since the polarization of the emitted light is confused due to the birefringence or the action of reflection and refraction of the condensing prism film or the diffusion sheet.    (Patent Document 1) U.S. Pat. No. 5,764,322    (Non-Patent Document 1) SIDO2 DIGEST P1236 to P1239
Further, the above-mentioned LED light sources may sometimes be arranged to have a predetermined space with a display area 21 as shown in FIG. 22. This is because dark sections 32 are formed between the LED light sources 31. Therefore, a dead area 33 of several millimeters is formed between the emitting surfaces of the LED light sources 31 and the display area 21 for preventing that the dark sections are formed on the irradiating area of the liquid panel. The dead area 33 is required to be formed as described above, whereby the size of the backlight increases by this area.
Moreover, in the conventional chip-type LED, there exists light that is incident on the emitting surface with an angle during when light is guided in the lamp body made of resin to reach the emitting surface. The light reaching the emitting surface is refracted and reflected based upon the Snell's low, whereby a part of the light reaching the emitting surface is reflected on the emitting surface to be transmitted again through the lamp body. Therefore, the light is reduced during the aforesaid repeated reflection, resulting in producing light that is not emitted. Accordingly, the conventional chip-type LED has a problem of low light take-out efficiency as an LED light source.
On the other hand, in the frontlight, the illumination device is arranged between the reflective-type liquid crystal panel and a display user, so that it is impossible to form a diffusion pattern, as formed in the backlight, on the light-guiding plate or to dispose a diffusion sheet. It is, therefore, difficult to eliminate non-uniform brightness of the light source. Accordingly, the light incident on the light-guiding plate is required to have uniform distribution in advance from the edge surface of the light-guiding plate. Therefore, a linear light-guiding member is arranged at the edge surface of the light-guiding plate and the LED light source is arranged at the edge surface of the linear light-guiding member.
This linear light-guiding member 35 is, as shown in FIG. 23, for introducing uniform light on a light-guiding plate 20 by using an LED light source 34, that is a point light source, as a linear light source. The back surface of the linear light-guiding member 35 has a prism structure for efficiently introducing light on the light-guiding plate 20 from the LED light source 34. Further, a reflector (not shown) is arranged at its outer periphery for efficiently combining light to the light-guiding plate 20. The arrangement of this linear light-guiding member 35 allows the light incident on the linear light-guiding member 35 from the LED light source 34 to transmit through the linear light-guiding member 35, whereby approximately uniform light is emitted toward the light-guiding plate 20. As a result, light having approximately uniform distribution can be emitted toward the liquid crystal panel 36 from the light-guiding plate 20 without using the diffusion sheet.
The light emitted from the LED light source 34 is impinged on the light-guiding plate 20 via the linear light-guiding member 35, so that it is reduced during the transmission through the linear light-guiding member 35, and hence, the light incident on the light-guiding plate 20 from the linear light-guiding member 35 becomes approximately a half of the light emitted from the LED light source 34.
If the cannonball-shaped lamp-type LED frequently used for popular electronic equipment is used for the illumination device of the liquid crystal display device, the light emitted from the LED light source is not efficiently incident on the light-guiding plate, since the emitting surface has a convex shape. Further, the shape of the irradiated surface of the light-guiding plate and the shape of the emitting surface of the LED light source do not agree with each other, thereby entailing a problem of deteriorating light incident efficiency on the light-guiding plate.
Further, among these types of LEDs, those disclosed in the patent documents 2, 3 and 4 described below have been well-known as those wherein light emitted from the emitting surface becomes approximately parallel.    (Patent Document 2) Japanese Unexamined Patent Application No. H10-335706    (Patent Document 3) Japanese Unexamined Patent Application No. 2002-134793    (Patent Document 4) Japanese Unexamined Patent Application No. H07-211940
Each of LEDs disclosed in the patent documents (patent documents 2 and 3) has a hemisphere-shaped reflection surface such that light emitted from a light-emitting surface of a light-emitting device is made approximately parallel with the reflection surface. Therefore, the LED disclosed in the aforesaid patent documents has a circular-shaped emitting surface seen from the front (seen from the irradiated surface) If this is used for the illumination device of the liquid crystal display device, the shape of the edge surface of the light-guiding plate and the shape of the emitting surface of the LED light source do not agree with each other, thereby entailing a problem of deteriorating light incident efficiency on the light-guiding plate.
Moreover, in case where the plane light-emitting type LED disclosed in the patent document 4 is used for the illumination device of the liquid crystal display device, light is not emitted from an electrode section to which the LED is mounted or from an electrode section that connects the LED and an external electrode. Therefore, if it is used for a light-emitting lamp of the illumination device, dark lines are observed in a line or in a band, thereby entailing a problem of remarkably deteriorating display quality.
Further, light is not emitted from the electrode area formed for establishing external electrical connection, thereby entailing a problem of reducing quantity of light.